The effects of selenium deficiency on the antioxidative status of erythrocytes from male SAM-R/1 mice were studied. The erythrocytes were obtained from mice fed Torula yeast-based, Se-deficient and Se-adequate diets for one year. The erythrocytes obtained were separated into 4 fractions of different cell density by densitygradient centrifugation, and the respective fractions were compared for activities of glutathione peroxidase (GSHPx), superoxide dismutase and catalase and for the levels of oxidized protein. Se deficiency depressed GSHPx activities significantly (about 90%) in all 4 density fractions, but depressed superoxide dismutase and catalase activities non-significantly in the respective density fractions and also in the whole erythrocyte fraction. The levels of oxidized protein were significantIy higher in the 3 low-density fractions from Se-deficient mice than in the corresponding fractions from Se-adequate mice. These results indicate that Se deficiency impairs cellular antioxidative status, inflicts oxidative damage on erythrocytes, and accelerates their aging.